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London 1944. Kisenga, a gifted composer and pianist, performs his latest work Baraza in the gilded setting of a concert hall. It is a farewell concert, because Kisenga is returning to Africa, his homeland, to assist the District Commissioner in the important work of health care. It is fifteen years since he left Africa and though Kisenga is glad to be returning he is torn by his dedication to English music.

Tanganyika (Tanzania). Kisenga is met by Mr Randall, the District Commissioner (DC), and taken on a tour of the district. En route they pick up Professor Gollner, a scientist. The DC explains the problems they face. An outbreak of sleeping sickness is moving across Tanganyika and has almost reached Marashi, Kisenga's home village. The solution is to transfer the population of 25,000 to a new settlement on higher ground and set fire to the bush to destroy the Tsetse fly that carries the sickness. Kisenga will be an invaluable bridge in communicating with the people, his kinsmen. The final member of the team is a new female doctor, Doctor Munro.

Kisenga finally arrives at Marashi, where he is reunited with his mother, father, sister Saburi and Akbram, his old teacher. Saburi is engaged to a young man named Ali, an assistant at the dispensary. Kisenga is summoned to meet the Chief.

Margoli, a witchdoctor, is a powerful influence on Chief Rafi. He informs Kisenga that they have no intention of moving to a new settlement; nor do they trust the white man's medicine. Margoli is particularly hostile to Kisenga, who he calls a white man with black skin. Many of the villagers believe Margoli, including Kisenga's own family. Later that night Margoli and his men perform a ritualistic animal sacrifice to protect the land from the sickness.

Kisenga settles into his new life, teaching music at the local school and helping Doctor Burton get the message across to the people. He is composing a classical score for the children based on African music.

One day at the dispensary, Doctor Burton finds evidence that the Tsetse fly has moved even closer to Marashi. She wants to do some blood tests on the villagers to see how far the sickness has spread. Ali, Saburi's fiancé, volunteers, as do Saburi and her father. Margoli warns the people that when you allow someone to take your blood you are putting your life in their power.

Margoli sabotages the bridge across the river. His threats are also effective in driving the people away from the dispensary. It seems unlikely that the DC, Doctor Burton and Kisenga will be able to persuade the villagers to move.

Kisenga's father becomes seriously ill - confirmation, it seems to the locals, of Margoli's prophecy. Doctor Burton examines the old man and diagnoses terminal malaria. When Kisenga's father dies, someone torches the dispensary.

The DC confronts Margoli and challenges him to try and kill him with his magic, but Margoli refuses: he seeks no power over white people. Kisenga makes the same challenge to Margoli and it is accepted. Margoli predicts that Kisenga will die before the new moon rises, two or three weeks hence.

Margoli begins to cast spells against Kisenga, who becomes troubled by nightmares and anxiety. Kisenga is also driven to breakdown because he feels responsible for his father's death, and he is keenly aware of his isolation from the villagers. He decamps to the Colonial manor house, where Doctor Burton gives him medication. But Kisenga is dying, and by morning he is unconscious.

Doctor Burton gathers the children's musical ensemble. They perform Kisenga's music outside the window. Kisenga opens his eyes; he is going to be ok.

The clearing of the village begins: huts are set on fire and a convoy of villagers leave for their new settlement in the mountains.